Bad Vibrations (from my rudder)

L

Laser76489

Member
Hi All

I have recently aquired a 25 year old but very lightly used Laser # 92716. I have had it out a few times in 10-15 Knot wind and have noticed that I get very loud hum and vibration from the rudder. I am woundering if there is anything that I can do to stop this. I have 2 other lasers niether of them has a hum as bad as this. I have tried switching the rudder for one of the ones from the other boats and the problem is still there. So it is therefore a problem relating to the hull. I have a very old Laser 1488 with some hum in the rudder and a 79 Laser # 76489 that I raced in the 80s and it has no hum at all. My sailing in Tornado cats has drilled into me that hums and vibrations are bad and slow you down. Is this the case for Lasers or should I just sail and put up with it??
 
Just curious, does it hum on all points of sail?
Laser76489 said:
Hi All

I have recently aquired a 25 year old but very lightly used Laser # 92716. I have had it out a few times in 10-15 Knot wind and have noticed that I get very loud hum and vibration from the rudder. I am woundering if there is anything that I can do to stop this. I have 2 other lasers niether of them has a hum as bad as this. I have tried switching the rudder for one of the ones from the other boats and the problem is still there. So it is therefore a problem relating to the hull. I have a very old Laser 1488 with some hum in the rudder and a 79 Laser # 76489 that I raced in the 80s and it has no hum at all. My sailing in Tornado cats has drilled into me that hums and vibrations are bad and slow you down. Is this the case for Lasers or should I just sail and put up with it??
Click to expand...
 
turn the boat upside down, put the daggerboard in and rudder on and sight from the bow, make sure rudder is on center and plumb. If not, adjust gudgeon until it is.

I didn't quite understand if the other rudder you tried also hummed on a different hull, just not as bad ? If that's the case, try and borrow someone's whose doesn't hum at all.

It may be a combo of blade shape and off center gudgeon.
 
More info to help or confuss


The humming is very bad on one boat(92716) no matter what blade I use.
The humming is there but not badly on 1488 regarless of what blade I use
The humming is not there on 76489 regardless of what blade I use.
 
Have you sanded down/tapered/sharpened the trailing edges of the rudder and dagger board?
 
Don't have an answer so maybe I should say nothing..

If it's only on downwind legs and not on reaches (where I have experienced humming when the boat is screaming) and based on the previous posts where you recorded the results of several variables, I would try the suggestion of looking at blade alignment (although I am confused on how one gets the dagger board aligned as mine is sloppy in the trunk).

The other thing is that there may be something causing a hydrostatic wave amplification - perhaps there is turbulence being created in the front that joins with another underwater wave being created in the stern to essentially create a larger more powerful wave. If you remember your high school physics experiments or watch what happens when the waves from one power boats wake on a smooth surface encounter another wave you can see a larger wave result at the intersection.

This doesn't fix your problem but may be there is something going on with the hull and rudder alignment?

Let us know what solves the problem!

After watching the Tour de France and the wind tunnel tests that cyclists use, perhaps AMD will not some time in a wind tunnel :)
 
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